U.S. Pat. No. 4,505,952 (Chambley) says: "The line used in fly fishing is conventionally of large-diameter braided construction, generally having an outer coating of plastic applied thereon. The diameter of this line is on the order of 1/32 to 1/16 inch. It is the weight of the line, not that of the lure, whose forward momentum propels the lure and which by slippage of the predetermined amount of slack line through the rod guides, extends the casting distance. It is generally desirable that the line used in fly fishing float on top of the water's surface. It is for this reason that there has been for many years a practice of coating the heavy braided fly line with a wax-like substance. This has the dual purpose of cleaning the line of debris, and simultaneously coating the line with a high surface tension wax-like substance which causes the line to float" (col. 2, lines 7-25). In addition to the above-described fly lines that have a braided core, other fly lines now on the market have a monofilament core. The aforementioned "outer coating of plastic" (here called the "casing") typically is polymeric, either poly(vinyl chloride) or poly(urethane). Because its casing is substantially cylindrical, a fly line can be called a "cylindrical fishing line."
The casing of a fly line can be filled with hollow microspheres to impart buoyancy. See U.S. Pats. No. 3,486,266 (Richardson et al.); 3,512,294 (Howald) and 3,868,785 (Foote). In the Foote patent, the substantially cylindrical casing is tapered. The casings of some fly lines are filled with metal particles to make them sink.
I believe that all fly lines now on the market have a lubricating dressing that enhances shootability, that is, the ability to propel a fly line and its fly. Lubricating dressings now on the market include topical silicones, fluorocarbons, and waxes that reduce the coefficient of friction (COF) of the fly line in contact with stainless steel of which most rod guides are made. Those dressings also can enhance flotation. After a period of use, the dressing wears off and the line becomes dirty. The user then cleans and dresses the dirty line with a piece of cloth to which a lubricating has been applied.
Fly lines, when new, usually can be used all day before they need to be cleaned and dressed, and this can be done at home when needed. After repeated use, most fly lines need to be cleaned and dressed more often, typically after about four hours of fishing, so that it may be necessary to dress the line in the field. This not only is inconvenient to the user, but there is a hazard of harming the environment by spilling the dressing.
The inconvenience of dressing a fly line in the field can be avoided when its polymeric casing has been pre-impregnated with a lubricating dressing that gradually migrates to the surface. A series of such fly lines is being marketed as Scientific Anglers.TM. Ultra.sup.3 by the company to which this application is assigned. However, to avoid problems associated with dressing conventional fly lines in the field, there continues to be a need to lengthen the time before it becomes because necessary to dress fly lines that have not been pre-impregnated with a lubricating dressing.
I am not aware of any study of the reflectivity of fly lines or the effect of the dressing on reflectivity, but there is a concern among fishermen that smooth cylindrical surfaces of fly line casings can cause reflections that could "spook" or frighten the fish away.